Generally, a method for acquiring an X-ray image by injecting a contrast medium into a blood vessel is used for confirming the state and position of the blood vessel in a body. In addition, in recent years, an angiography method for obtaining a tertiary image has also been developed. Examples of the angiography method include computed tomography (CT) angiography and magnetic resonance angiography (MRA).
In addition, a method for capturing a channel such as a blood vessel using an optical technique has also been conventionally proposed (refer to Patent Document 1). In an imaging system described in Patent Document 1, an interference light image is captured at a first timing using interference light which is light emitted from a light emission unit and reflected by an object, and a light emission image of light emitted from the object is captured at a second timing. Furthermore, a method for improving positional accuracy of a blood vessel using an image process has also been proposed (refer to Patent Document 2).
As described above, in recent years, various methods with the use of optical techniques have been developed in the medical field and the like, and detection accuracy thereof has also been increasing year by year. For example, Patent Document 3 discloses a technology for improving signal detection accuracy by having an optical means for generating a plurality of beams in a laser doppler perfusion imaging device including a laser light source, an image detector, and a signal detector.
Incidentally, in relation to the imaging technologies with the use of optical techniques, a reduction in the detection accuracy caused by occurrence of various noises is a matter of concern, and speckle interference is known as one of the noises. The speckle interference is a phenomenon in which a spotty swaying pattern appears on an irradiated surface in accordance with an uneven shape of the irradiated surface.
A technology for suppressing the speckle noise has also been developed. For example, Patent Document 4 discloses an illumination technology, that is, an illumination device that obtains illumination light by mixing light in a first wavelength band and light in a second wavelength band. Specifically, a light source that emits the light in the first wavelength band is a broad area type semiconductor laser, and the illumination device includes a high-frequency wave superimposing means for superimposing a high-frequency signal on a driving current that is supplied to the semiconductor laser, and causing the semiconductor laser to perform multimode oscillation, whereby illumination light without a speckle interference noise can be stably obtained.
In addition, Patent Document 5 discloses a technology for reducing the influence of the speckle noise on obtained image information by forming a light guide using a fiber bundle that is a bunch of a plurality of optical fibers having an optical path length difference equal to or greater than the coherence length of excitation light, and by providing a noise reduction device including the fiber bundle.